Laboratory research suggests the drug candidate blocks the new coronavirus from replicating, Pfizer research-and-development chief Mikael Dolsten said in an interview. The findings indicate the experimental drug could slow or stop the spread of the virus in patients with mild-to-moderate symptoms, though human testing will be necessary for proof.

The early progress is among several developments in Pfizer's multipronged efforts to find coronavirus drugs and vaccines.

Pfizer will also start testing its approved rheumatoid-arthritis drug Xeljanz in coronavirus patients in Italy this week to see whether the therapy has a benefit, Dr. Dolsten said. And the company is planning to publish research on whether one of its antibiotics helps.

In addition, Pfizer has been working with BioNTech SE of Germany to develop a vaccine based on an emerging gene-based technology. Pfizer said it plans to move into clinical trials as early as the end of this month with four different vaccines simultaneously, and aims to move the best one forward in future studies.

"I feel confident that we will win, battle by battle, to turn around this viral war against our society," Dr. Dolsten said.

There are no approved medicines to treat or prevent the new coronavirus, which causes the disease known as Covid-19. The testing required to assure the drugs and vaccines work safely is expected to take months.

Dozens of companies and university researchers have been hustling to develop therapies or vaccines against the virus. More than 140 are in development world-wide, most in early stages, including about a dozen already in clinical trials, according to Informa Pharma Intelligence.

Among the other drugmakers working on treatments are Eli Lilly & Co., Gilead Sciences Inc. and Takeda Pharmaceutical Co.

Pfizer, based in New York City, assembled a team of 50 researchers from various departments to work on the coronavirus, and ramped up projects exploring different potential medicines.

One challenge the drugmaker confronted was reconstituting antiviral research after disbanding the department in 2009. To limit interactions among personnel, the company's coronavirus team has yet to meet in person.

The team reviewed compounds that have shown activity against other coronaviruses, including severe acute respiratory syndrome, or SARS, Dr. Dolsten said.

Pfizer's lab research suggests that its lead drug and similar candidates are strong blockers of a key enzyme, known as a protease, that helps viruses replicate, Dr. Dolsten said. Pfizer plans to begin studying the lead drug in patients as early as August, several months ahead of schedule.

"Time is urgent here," he said. "Every hour, every day counts."

To be able to make sufficient supplies of the drug candidate for testing, Pfizer several weeks ago bought the raw materials needed to manufacture the medicine, said Charlotte Allerton, who leads Pfizer's medicine design.

Pfizer expects the trial in Italy evaluating Xeljanz's effect on coronavirus patients to finish in July. The company says the drug could help damp an overactive immune response that occurs in some patients and can lead to respiratory failure and death.

Other anti-inflammatory drugs, such as Roche Holding AG's Actemra, have shown signs of working on coronavirus patients who suffer from respiratory problems. Xeljanz functions differently than Actemra, and could be an alternative for patients who don't respond to anti-inflammatory drugs such as Roche's drug, Dr. Dolsten said.

Pfizer expects to publish its findings on the anticoronavirus powers of the antibiotic azithromycin, which Pfizer sells under the brand name Zithromax. Many doctors, lacking proven options, are treating Covid-19 patients with the antibiotic and antimalaria drugs.

Pfizer also plans to begin two studies with the U.K.-based Liverpool School of Tropical Medicine to investigate whether coronavirus patients are at higher risk of developing pneumococcal pneumonia and if having both infections leads to more-severe disease.

The company's partnership with BioNTech is exploring a vaccine based on the gene-based technology known as messenger RNA. Messenger RNA, or mRNA, carry instructions from DNA to the body's cells to make certain proteins.

No mRNA vaccines have been approved. Moderna Inc. and Inovio Pharmaceuticals Inc. have begun testing their mRNA coronavirus vaccines in patients.

Last month, Pfizer said it would make some of its research on the virus available publicly online for other researchers. The drugmaker also said it would offer available manufacturing capacity to other companies, if they win approval and require help making their medicines.